The present invention relates to a pulse generating circuit composed of MOS IGFETs (metal-oxide-semiconductor field-effect transistors).
A conventional circuit of the same general type to which the invention pertains is shown in FIG. 1. In this figure, transistors Q.sub.1, Q.sub.3, Q.sub.5, Q.sub.7 and Q.sub.10 are depletion-type devices, while transistors Q.sub.2, Q.sub.4, Q.sub.6, Q.sub.8 Q.sub.9, Q.sub.11, Q.sub.12, and Q.sub.13 are enhancement-type devices. Transistors Q.sub.1 through Q.sub.6 are connected in the configuration of a three-stage inverter, the transistors Q.sub.7, Q.sub.8, and Q.sub.9 in a NOR circuit, the transistors Q.sub.12 and Q.sub.13 in a NAND circuit, and the transistors Q.sub.10, Q.sub.11 and Q.sub.12 in a second NOR circuit.
In operation, with reference also to the timing chart of FIG. 2, the input signal A is delayed and inverted by the inverter circuit composed of the transistors Q.sub.1 through Q.sub.6 to produce a signal B, which is delayed and inverted with respect to the signal A. By forming the NOR of the signals A and B, a pulse signal C is produced. Further, by forming the NAND of the signals A and B with the NAND gate formed of the transistors Q.sub.12 and Q.sub.13, low-going pulses are produced at times between the pulses of the signal C. By forming the NOR of the signal C with the NAND product of the signals A and B using the transistors Q.sub.12 and Q.sub.13, an output signal D is produced as shown in FIG. 2.
To change the pulse width of the signal D, the number of stages of the inverter circuit can be changed (so long as an odd number of stages is maintained).
Although the circuit of FIG. 1 is capable of producing an output pulse signal as desired, nevertheless, it is disadvantageous in that its implementation requires more transistor devices than is desirable. Accordingly, its overall power consumption is higher than is desirable, and also the chip area required for the circuit is large. Another disadvantage is that the circuit layout must be changed to vary to pulse period.